The present invention relates to a stabilizer for motor vehicles, having a divided torsion bar, the divided parts of which can be coupled or connected to one another at their mutually adjacent ends by means of a clutch arrangement which can be controlled as a function of the transverse acceleration of the vehicle or a parameter correlated with the transverse acceleration.
Stabilizers are customarily used to couple the wheel suspension of a wheel elastically on one side of the vehicle to the wheel suspension of the corresponding wheel on the other side of the vehicle in such a way that, when one wheel is compressed, the suspension of the other wheel is stressed in the compression direction. When the vehicle is cornering, its side tilt towards the outside of the curve is thereby reduced because the particular wheel toward the outside of the curve is additionally supported by the suspension of the wheel toward the inside of the curve and the wheel toward the inside of the curve is forced somewhat in the compression direction relative to the vehicle body.
In straight line driving on the other hand, the stabilizer should have as little effect as possible on the vehicle or the suspension behavior of the vehicle. However, this can essentially only be guaranteed when the vehicle is travelling over transverse furrows or the like and the wheels on both sides of the vehicle are therefore in each case simultaneously stressed in the compression direction relative to the body. The influence of the stabilizer here is negligible. However, when the roadway is uneven in such a way that a wheel on one side of the vehicle is forced in the compression direction while the corresponding wheel on the other side of the vehicle must be moved in the rebound direction in order to maintain the desired ground contact, the ride comfort is impaired by a stabilizer, since the stabilizer attempts to counteract mutually opposing movements of the wheels coupled by the stabilizer relative to the vehicle body.
It is known from German Published Patent Application (DE-AS) No. 1 105 290 that a stabilizer having a divided torsion bar can be installed, the parts being connected together in the manner of a hydraulic clutch which is controlled as a function of the centrifugal force or the steering of the vehicle. This provides the possibility of rendering the stabilizer inoperative by opening the clutch.
It is known from German Published Unexamined Patent Application No. (DE-OS) 2 849 015 that an undivided stabilizer can be supported on the vehicle body by means of compliant elements, more precisely by means of hydraulic vibration dampers. The bearings of the stabilizer thus have a more or less great mobility relative to the vehicle body. In this arrangement, the hydraulic vibration dampers are of a design such that, in a central or normal position of the stabilizer, they have a negligible damping resistance. The consequence of this is that, in a range near to its central or normal position, the undivided stabilizer is to the greatest possible extent inoperative. During sudden avoidance maneuvers or during cornering on an uneven roadway, this can be disadvantageous.
Therefore, it is an object of the present invention to provide a stabilizer which, during cornering and avoidance maneuvers , is sufficiently effective in every case and otherwise leaves the suspension behavior of the vehicle as far as possible unimpaired in order to ensure a high degree of ride comfort.
This object is achieved in the case of a stabilizer of the type mentioned at the outset because the clutch arrangement permits play of the parts of the torsion rod, which play can be controlled as a function of the actual and/or expected transverse acceleration of the vehicle.
The invention is based on the general idea that a stabilizer should be effective to differing degrees depending on the extent to which transverse forces are acting on or are expected to act on the vehicle. At the same time, according to a preferred embodiment of the invention, provision is made to reduce the play allowed in each case if the actual transverse forces or those to be expected increase. Thus, according to the invention, it is possible to make the efficiency of the stabilizer dependent on the magnitude of the transverse forces.
The transverse acceleration of the vehicle, in accordance with one embodiment of the present invention, is preferably determined by computation. A transverse acceleration can, for example, be determined from the particular steering angle and/or the particular rate at which the steering angle changes and the particular driving speed of the vehicle. To be precise, the value for the transverse acceleration calculated in this manner is the value of the acceleration which is to be expected in each case, the value occurring inasfar as possible during slip-free driving or in the case of good traction. Since a vehicle can only react to changes in the steering angle after a certain time delaY, the transverse acceleration of the vehicle changes after a corresponding time delay following a change in steering angle. If desired, the computer which calculates the transverse acceleration from the steering angle or the rate at which the steering angle changes and also the driving speed can operate with a corresponding delay. In general, however, it is expedient and advantageous if the computer operates without a delay or with a negligible delay. When the vehicle is then steered out of a straight line into a curve, the permissible play of the parts of the torsion rode is then reduced to a greater or lesser extent as a function of the driving speed and the steering angle or of the rate of change of the steering angle, i.e., the stabilizer is prepared and matched to the transverse acceleration of the vehicle to be expected.
Furthermore, provision is expediently made to control the clutch arrangement as a function of data on the tires fitted to the vehicle, the loading condition or the like.
Furthermore, provision can be made to couple the parts of the stabilizer with controllable non-positive engagement, that permits slippage between the parts of the stabilizer above a certain threshold value, the non-positive engagement as a rule increasing as the values for the actual or expected transverse acceleration of the vehicle increase, a slip-free coupling of the stabilizer parts being guaranteed at higher values of the actual or expected transverse acceleration.
In a particularly preferred embodiment of the invention, provision is made to provide a servomotor as clutch arrangement or as part thereof, which servomotor allows clutch-facing ends of the parts of the stabilizer to be displaced relative to one another or be subjected to a positioning force in order to counteract a side tilt of the vehicle towards the outside of the curve. In this embodiment of the invention, account is taken of the fact that the stabilizer parts which have been uncoupled from one another during straight line driving of the vehicle can be displaced comparatively far from a central position relative to one another if the wheel associated with the stabilizer on one side of the vehicle is compressed and the wheel on the other side rebounds. This displacement of the stabilizer parts can be reversed by means of the servomotor in order to render the stabilizer fully operative, in the event of cornering immediately following the compression and rebounding, respectively, of the wheels.
It is also fundamentally possible here to displace the stabilizer parts so far with respect to one another by means of the servomotor that the vehicle body tilts only negligibly or not at all towards the outside of the curve.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.